Aircraft gas turbine engines generally employ exhaust or ejector nozzles having flaps and seals that are used to contain exhaust flow from the engine and use thrust to propel the aircraft. The nozzle is generally designed for supersonic operation and includes a convergent portion for accelerating the exhaust airflow at the nozzle throat and a divergent portion for accelerating the exhaust airflow supersonically.
Cooling of the nozzle is generally required to provide thermal protection to the nozzle and fire protection to the aircraft engine. Cooling is generally provided by diverting a source of nacelle or ambient air around the aircraft engine and into the divergent portion of the nozzle using an ejector. The ejector is generally located in the divergent portion of the nozzle such that the exhaust airflow, being at a higher velocity and higher pressure, draws lower velocity and lower pressure cooling air into the nozzle to cool the nozzle.
Preventing the exhaust airflow from escaping the aircraft engine and migrating into a nacelle where the accumulated exhaust airflow may combust or cause a fire or explosion is also important. The ejector reduces the likelihood of the exhaust airflow migrating into a nacelle by withdrawing air in the nacelle into the divergent portion of the nozzle.
However, present nozzles suffer from several disadvantages. For example, airflow from the nacelle is strongly dependent on the nacelle inlet characteristics, the nozzle schedule, the ejector characteristics, and the flight envelope of the aircraft. Thus, it is generally difficult to provide all the required nacelle airflow in all regions of the flight envelope without having a negative impact on aircraft and/or engine performance or negative impacts to airframe strength. For example, particular flight envelope conditions may result in a reduced or negative pressure differential between the nacelle and the divergent portion of the nozzle, thereby reducing or reversing the airflow in the nacelle creating a fire hazard.